jpg or png for UIImage — which is more efficient?

Question

I am grabbing an image from the camera roll and then using it for a while as well as save it to disk as a PNG on the iPhone. I am getting the odd crash, presumably due to out of

Answer 1

1. is more memory then used by the UIImage after I reload it off of disk if I saved it as a PNG? => No, it's the same memory size if you import from 2 images that have same resolution and same number of channels. (such as RGBA)
2. is it possible the act of saving as PNG uses up more memory transiently during the saving process? => No, it only effect your disk memory.